/*
  ID: nemokin1
  PROG: barn1
  LANG: C++
*/

#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
 
using namespace std;
 
#define REP(i,n) for(int i=0; i<(n); ++i)
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define FORD(i,a,b) for(int i=(a);i>=b;--i)
#define FOREACH(it,c) for(typeof((c).begin()) it=(c).begin();it!=(c).end();++it)
#define ALL(c) (c).begin(),(c).end()
 
#define debug(x) cerr<< #x << " = " << (x) << "\n";
#define debugv(v) cerr << #v << " = "; FOREACH(it,v) cerr << *it <<","; cerr << "\n";
#define SIZE(a)  (int(a.size()))
 
template<typename T> inline void checkMax(T& a, T b) {if (b>a) a=b;}
template<typename T> inline void checkMin(T& a, T b) {if (b<a) a=b;}
 
typedef long long LL;
typedef vector<int> VI;
typedef vector<string> VS;
typedef long double ld;
const int INF = 1000000000;

int main() {
    freopen("barn1.in","r",stdin);freopen("barn1.out","w",stdout);
    int Board,N;
    int ret = 0;
    
    cin >> Board;
    cin >> N;
    cin >> N;
    vector<pair<int,int> > vp;
    REP(i,N){
	int t;
	cin >> t;
	vp.push_back(make_pair(t,t));
    }
    sort(ALL(vp));

    if(Board >= N) cout<<N<<endl;
    else{
	
	for(;;){
	    int min = INF;
	    int mini = 0;
	    int M = SIZE(vp);
	    //FOREACH(it,vp) cerr<<it->first<<":"<<it->second<<endl;
	    if(M == Board) break;

	    int i = 0;

	    for(i = 0; i < SIZE(vp)-1; i++){
		if(vp[i+1].first-vp[i].second < min){
		    mini = i;
		    min = vp[i+1].first-vp[i].second;
		}
	    }
	    vp[mini].second = vp[mini+1].second;
	    vp.erase(vp.begin()+mini+1);
	}
	FOREACH(it,vp){
	    ret+=(it->second-it->first+1);
	}
	//FOREACH(it,vp) cerr<<it->first<<":"<<it->second<<endl;
	cout<<ret<<endl;
    }
    
    exit(0);
}
    
